Augmented thermal bus

ABSTRACT

The present invention is directed to an augmented thermal bus. In the present design a plurality of thermo-electric heat pumps are used to couple a source plate to a sink plate. Each heat pump is individually controlled by a model based controller. The controller coordinates the heat pumps to maintain isothermality in the source.

ORIGIN OF INVENTION

The invention described herein was made in the performance of work undera NASA contract and is subject to the provisions of Section 305 of theNational Aeronautics & Space Act 1958, as amended, (42 U.S.C 2457).

STATEMENT OF COPENDENCY

This application is a division of application Ser. No. 08/081,891 whichwas filed Jun. 25, 1993, now U.S. Pat. No. 5,349,821.

FIELD OF INVENTION

The present invention is directed to a thermal bus for dissipating heatby using a plurality of individually controlled thermo-electric heatpumps (TEHP). Each heat pump individually controls a region on a source.The orchestrated control of all the TEHP unit, is performed by a modelbased controller.

In thermal bus arrangements found in the prior art, a baseplate housingelectronics is coupled to a coldplate through a thermo-electric heatpump. Integral with the coldplate is a fluid loop attached to radiatorpanels which discharges the energy convected at the coldplate. Theworking fluid in the coldplate acts as a shunt to couple the electronicsto remotely located radiator panels. Each component has an associatedthermal resistance which, as a function of design, is a measure of thetemperature drop across that component for a given heat load. Waste heatis dissipated in these systems through conduction. The waste heat inNASA prior art systems is not upgraded to a higher temperature,therefore these systems require large radiator panels to reject theheat.

While the prior art design of a thermal bus is simple and reliable, theoverall effectiveness of the device is diminished by the radiator andliquid inventory weight restrictions, in conjunction with limitedcoldplate isothermality.

When feedback control has been applied in the prior art thermal busunits, it has taken the form of PID controllers. Although the PIDcontroller takes temperature variation (set point temperature minus theactual) into account, in an attempt to maintain isothermality, it is alimited control mechanism.

Traditionally, these PID controllers have been used in the prior art, tooffer a single point of control. The concept can be extended to severalPID loops, thereby controlling several set points in the plane of asource. However, the extension of PID controllers in this fashion, doesnot compensate for conduction heating, in the plane of the source. Theindividual heat control actions between PID units would not becoordinated. Therefore, in performing heat control, thermal bus designsin the prior art do not take the heating or cooling that is provided bythe other TEHP units, into account. As a result, these systems couldonly offer coupled heat control.

It is, therefore, an object of the present invention to create a thermalbus with a higher level of isothermality in a heat source or baseplate.

It is a further objective of the present invention to upgrade the wasteheat produced by the system thereby reducing the surface area requiredfor a radiator.

It is still a further object of the present invention to individuallycontrol areas of a heat source relative to a sink by using a pluralityof thermo-electric heat pumps.

It is still yet a further object of the present invention to achievedecoupled temperature control of a thermal bus by using a model basedfeedback control system.

DESCRIPTION OF THE RELATED ART

U.S. Pat. No. 4,848,090 by Peters discloses an apparatus and a methodfor controlling the temperature of a semiconductor device.

U.S. Pat. No. 3,481,393 by Chu discloses a cooling system for modularpackaged electronic components.

U.S. Pat. No. 3,438,214 by Schmittle discloses a thermoelectrictemperature control system for cooling and heating of a substanceflowing therethrough.

U.S. Pat. No. 4,610,142 by Davis discloses an apparatus and method forcontrolling the temperature of a reagent refrigerator.

U.S. Pat. Nos. 2,844,638 and 2,203,857 by Lundenblad, both disclose athermoelectric heat pump which is made of a compact thin panelconstruction.

U.S. Pat. No. 4,310,047 by Branson discloses a device for maintaining anobjective at a given temperature by means of a thermoelectric heat pumpheld between a thermally conductive member and a heat sink.

U.S. Pat. No. 5,022,928 to Burst discloses a TEHP comprising p-type andn-type semiconductor film conductive elements selectively patterned onsubstrates.

SUMMARY OF THE INVENTION

The present invention is an augmentation of a conventional single-phasethermal bus with an interstitial thermo-electric heat pump (TEHP). Thethermo-electric heat pump is a solid-state direct energy conversiondevice. Since the TEHP does not have any moving parts it is structurallyand thermally robust making it uniquely suited for temperature coolingin a hostile environment.

In the present invention, a modular thermal bus includes targetelectronics which are mounted on a baseplate forming a source. Aplurality of TEHP devices are compression mounted between the source anda sink. The sink has a fluid loop which is coupled to radiator panels.Heat is transported from the source, through the heat pumps to the sinkwhere the fluid loop coupled between the sink and the radiator panelsuses the radiator panels to dissipate the heat.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, advantages, and novel features of the invention will bemore fully apparent from the following detailed description when read inconnection with the accompanying drawings in which:

FIG. 1 displays a schematic of a thermo-electric heat pump.

FIG. 2 displays a schematic of a TEHP-assisted thermal bus.

FIG. 3 displays the connection between the cold plate of theTEHP-assisted thermal bus and a feedback controller.

FIG. 4 displays a conceptual graph of the TEHP-assisted thermal buswithout TEHP assistance.

FIG. 5 displays a conceptual graph of the TEHP-assisted thermal bus withTEHP assistance.

FIG. 6 is a block diagram of the feedback control method performed inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 displays the thermo-electric heat pump module. A hot junction 10and a cold junction 22 sandwich the terminal leads 12, 14, 16, a p-typejunction 18 and a n-type junction 20. The hot junction 10 is connectedto a baseplate or source, and the cold junction 22 is attached to acoldplate or sink. When power is applied between the terminal leads 12,14 and 16, heat will flow across an adverse temperature gradient fromthe hot junction 10 to the cold junction 22 thereby dissipating the heatdeveloped by the electronic components.

FIG. 2 displays a schematic view of the TEHP-assisted thermal bus. Acoldplate or sink 26 is coupled to a fluid loop formed by 60 and 62which enables fluid to circulate through the coldplate, therebydissipating heat. A plurality of quadrants 30, 32, 34, 36, 38 and 39house a plurality of thermo-electric heat pumps denoted by 40, 42, 44,46, 48, and 49, respectively. A negative polarity busbar 64 is alsoattached to the coldplate 26, thereby enabling a negative voltage acrossthe coldplate 26.

The thermo-electric heat pumps 40, 42, 44, 46, 48, and 49 are sandwichedbetween the coldplate 26 and the baseplate or source 28, therebyoffering a conductive heat pathway. Electronics are located in thematching quadrants 50, 52, 54, 56, 58 and 59 of the baseplate 28,thereby enabling each quadrant to be controlled by a TEHP unit denotedby 40, 42, 44, 46, 48 and 49, respectively.

A busbar for carrying a positive current 66 is also attached to thebaseplate 28. By placing a positive polarity across the source orbaseplate 28 and a negative polarity across the sink or coldplate 26,voltage is applied across the TEHP devices 40, 42, 44, 46, 48 and 49.The applied voltage would cause heat to flow from the source orbaseplate 28 to the sink or coldplate 26 across an adverse temperaturegradient.

FIG. 3 displays a schematic view of the coldplate 26 with quadrants 30,32, 34, 36, 38, and 39 each controlled by a controller 109, throughconnections 80, 82, 84, 86, 88, and 89 respectively.

FIG. 4 displays a schematic flow diagram of the methodology used in thecontroller 109 presented in FIG. 3. The controller 109 receives anoutput of temperature readings generated by thermocouple or thermistorslocated in the quadrants 50, 52, 54, 56, 58 and 59 of the baseplate, 28shown in FIG. 3. The temperature readings are transported through thehard-wired connections 90, 92, 94, 96, 98 and 99, depicted in FIG. 3.The temperature readings are inputed into the controller 109 shown inFIG. 4, at location 160, as an array of process temperatures.

According to the present invention, temperature, voltage and currentmeasurements are taken of each quadrant of the source. These parametersalong with several other parameters define the process of the augmentedthermal electric heat pump, which is denoted by 150.

A mathematically based model of the augmented thermal bus is alsomaintained by the controller 109. The modelled process is denoted by155. Both the actual process 150 and the modelled process 155 producearrays of temperature outputs at 160 and 165, respectively. The processtemperature array at 160 and the modelled temperature array at 165, aresummed at 170. When there is a difference between the processtemperature array 160 and the modelled temperature array at 165, anerror array occurs at 175. This error array represents a deviation fromthe expected operation of the system as described by 155. The error intemperature 175 is then summed with a set point temperature array at115. The set point temperature array is an array of temperature valuesset for quadrants 50, 52, 54, 56, 58 and 59. The expected inverse modelarray 120 represents a deviation from the set point temperature of thebaseplate. The expected inverse model array 120 serves as the input forthe inverse of the modelled process 125. The inverse of the modelledprocess augmented with a conditioning filter, 125 produces an output 130that tries to correct for the expected inverse model array 120. Theoutput from the inverse of the modelled process 130, is an array ofvoltages or currents used to control the TEHP devices, therebycompensating for the expected inverse model array, denoted by 120. Thevoltage change at 130 will serve as an input to both the actual processat 140 and the modelled process at 145. Changing the voltage or currentinputs 140 and 145 will result in an increase of the pumping capacity ofthe TEHP units, to accommodate for the change in isothermality.

In the case where there is no disturbance in the operation of theaugmented thermal bus, the process temperature array at 160 would equalthe model temperature array at 165. When these two values are summedthere would not be any error at 170 therefore, there would be no errortemperature at 175. Also, the value fed into the inverse model 125 wouldbe equal to the value of the set point temperature array 110. Since theset point temperature array at 110 are the values that the inverse model125 expects as input, there is no variation in the output voltage at130. Consequently, there would not be any change in the inputs to theprocess at 140 or the modelled process at 145. In the scenario givenabove, the the pumping capacity of the individual TEHP units would notbe altered.

As an example of a case where a disturbance does occur, in FIG. 3, afirst quadrant 50, a second quadrant 52 and a third quadrant 54 arecontrolled by a first TEHP unit 40, a second TEHP unit 42 and a thirdTEHP unit 44. If the second TEHP unit 42 were to fail, it would causequadrant 52 to increase in temperature. Due to conduction heating in theplane of the source, quadrants 50 and 54 would also increase intemperature. The thermocouple senses this activity and reports a T1representing the first temperature, a T2 representing a secondtemperature and a T3 representing a third temperature back to thecontroller through the hard wired connection 90, 92 and 94,respectively. These three values, T1 the temperature of quadrant 50, T2the temperature of quadrant 52 and T3 the temperature of quadrant 54would be fed back into our model at 160. When the process temperaturearray [T1, T2, T3] at 160 are combined with the model 160 temperaturearray [T1m, T2m, T3m] at location 170, the first temperature of theprocess (T1) will cancel the first temperature of the model (T1m). Thethird temperature of the process (T3) will cancel the third temperatureof the modelled process (T3m). However, the second temperature of themodel (T2), will not cancel the second temperature of the model (T2m).Therefore there will be a non-zero value T2e at 175, which represents anerror in the augmented thermal bus. The error temperature array [0, T2e,0] will be combined at 115 with the set point temperature array [T1sp,T2sp, T3sp]. As a result of the combination at 115, the inverse model125 will note a deviation in the set point temperature for the secondquadrant, since T2e will be subtracted from T2sp. Since the inversemodel 125 will receive a set point temperature that is lower than whatit expects (T2sp-T2e) for the second quadrant, the inverse model 125would vary the voltage outputs to the TEHP units surrounding thatquadrant would require a contingency instruction; after knowing thatTEHP/q2 failed the controller would define new objectives such as tocontrol the average temperature of all quadrants in the vicinity of thefailed quadrant to the average set point.

In our example, these two quadrants are physically represented by unit40 and 44 of FIG. 4. By increasing the pumping capacity of units 40 and44, voltage variations would be fed back into the process 150, throughinput 140 and to the modelled process 155, through input 145. Assumingthat the actual process 150 was just combined with the set pointtemperature back into the inverse process 125, we would experiencecoupled temperature control. However, by combining the modelledtemperature 165 with the actual temperature 160 and then feeding thetemperature error 175 back into the inverse of the model 125, decoupledcooling is achieved in the augmented thermal bus system.

A mathematical description would include the following:

T1--temperature in the first quadrant

T2--temperature in the second quadrant

T3--temperature in the third quadrant

q1--the inverse model of the first region

q2--the inverse model of the second region

q3--the inverse model of the third region

x--a scaler multiple

y--a scaler multiple

In the coupled case, the process temperature array is multiplied by thematrix of the process 150 to produce the following output: ##EQU1##

In this coupled representation, the inverse process will respond to T1,T2 and T3 individually through q1, q2, and q3 without ever accountingfor the temperature changes or disturbances occurring in other regions.However, by adding the inverse model 125 and developing q as the inverseof the modelled process 155, the following conceptual formulation wouldresult: ##EQU2##

Where q12 and q13 are some multiple of q22 and q33, respectively.

The result is a decoupled cooling process. The temperature in quadrant 1(T1), the temperature in quadrant (T2) and the temperature in quadrantthree (T3) will be adjusted taking the other temperature regions intoaccount, as displayed by the resulting decoupled vector, in equation 1(T1q₁₁ +xT2q₁₂ +yT3q₁₃).

FIG. 5. displays a conceptual view of the temperature flow in aconventional thermal bus. The electronics mounted on the baseplate,denoted by 210 functions as a source, generating heat at a temperature310. The baseplate denoted by 220 receives this heat at a slightly lowertemperature 320. In the conventional thermal bus the baseplate denotedby 220 would be directly coupled to the coldplate denoted by 230. Thecoldplate would experience another loss in temperature 330, as a resultof the conduction process. The loss in temperature would continuethrough the fluid loop 240 coupled to the coldplate, the radiatordenoted by 250 and culminating in the effective sink denoted by 260. Ineach of these steps, the heat flow due to conduction has an associatedtemperature drop 340, 350, and 351, respectively.

FIG. 6 displays the thermal bus with the thermo-electric heat pumps,located between the baseplate and the coldplate. The electronics 400 andthe baseplate 410 receive the convectional temperature drop, as denotedby 500 and 510. However, in the TEHP assisted thermal bus, a TEHPdenoted by 420 is placed between the baseplate 410 and the coldplate430. Therefore instead of experiencing a temperature drop between thebaseplate 410 and the coldplate 430, heat is pumped across an adversetemperature gradient from the baseplate 410 to the coldplate 430. Theresult is the increase in temperature from the temperature in thebaseplate 510, across an adverse temperature gradient 520, to thetemperature of the coldplate 530. The fluid loop coupled to thebaseplate denoted by 450 and the radiator 460, continue to decrease thetemperature from 550 to 560. The radiator 460 maintains the sametemperature of the effective heat sink 470. The radiator temperature 560is normally the same as the effective sink temperature 561.

The effective heat transfer coefficient is equal to the third power ofthe power of the radiator temperature (h˜T³). As a result, radiating ata higher radiator temperature requires a radiator with a smaller surfacearea. Therefore, the overall result of adding the TEHP to upgrade thewaste heat at 520, is a smaller radiator at 580.

Each TEHP unit will individually control an area on the source. When asmall direct current is applied to the TEHP devices, thermal energy ispumped from the source or baseplate to the thermal sink or coldplate,across an adverse temperature gradient. As a result, a TEHP unit will beresponsible for transferring heat from an individual quadrant on thesource, to the sink. Each of the TEHP units within a quadrant will beindividually controlled thereby enabling a controller to vary pumpingoperation of TEHP units either within the quadrant or surrounding thequadrant. As a result isothermality will be maintained as the fluid loopintegral with the coldplate, shifts to an increased sink temperature.

The operation of each of the TEHP units located within the predefinedquadrants will be controlled by a model-based feedback controller. Thecontrol system maintains isothermality by adjusting the TEHP heatpumping capacity to compensate for scheduled and unscheduleddisturbances in the thermal bus. The heat pumping capacity is adjustedwhile maintaining the local quadrant set-point temperature.

In general, any off-design or contingency operating conditions areconsidered unscheduled disturbance. Usually these unscheduleddisturbances are caused by parasitic heating in the target electronicsor variations in the fluid loop inlet temperature. In general, anydisturbances or variations in heat or power, may be considered ascheduled disturbance. For example, heating caused by the predictabledegradations in the electronic components.

The model-based control system used to control the TEHP units operate byfirst sensing a process temperature in each quadrant on the source orbaseplate. This process temperature array is combined with a modelledtemperature array to create a temperature error array. The system thencombines the temperature error array with the set point temperaturearray to produce the expected inverse modelled array, which is an arrayof set point temperature values, fed into an inverse model of theprocess. Any variation in the input of the inverse model, causes themodel to produce a change in the voltage or current output produced bythe inverse model. The result of a change of voltage or current is anincrease the pumping capacity of the TEHP units, located in the regionof the affected quadrant.

In the case where the set point temperatures are all equal, individuallyvarying the TEHP units will produce a uniform isothermal baseplate. Inthe event that one of the TEHP units completely fails, the controlsystem will perform load levelling to minimize variations inisothermality. As a result of using model based feedback control, theTEHP unit transfers heat from a quadrant, taking into account the otherindividually controlled quadrants, thereby maintaining isothermality inthe source. Therefore, convection heating in the plane of the sourceplate, is controlled with a decoupled control method.

For the TEHP units to transfer heat across an adverse temperaturegradient the TEHP requires a direct current with less than five percentripple. A current generator is used in the system to modulate thevoltage and current. The nominal voltage and current requirements perdevice are on the order of 0-0.5 volts and 10 amperes, respectively. Thebusbar requirements depend on the degree of control required. Forapplications where the individual TEHP units are controlled with asingle power source, the baseplate and coldplate would serve as thebusbar. While this design is very simple, redundancy and isothermalitycontrol are compromised. If groupings of devices or quadrants arepowered separately, each quadrant would require a segregated busbararrangement.

Independent of the number of controlled devices, a single power sourceis multiplexed with peer transistors operating under the command of themodel-based feedback control system. On command, the power isdistributed to a specified quadrant of devices, at a specified level,for a specified time, after which the power is switched off and divertedto the next quadrant of devices. The frequency of modulation isdependent on the allowed switching losses and the thermal capacitance ofthe TEHP and adjoining structure, along with the nature of the thermaldisturbance. Low weight structures have low thermal capacitance whichwould require an increased switching rate, which is desirable. However,an increased switching rate results in parasitic switch heating, whichis an undesirable feature.

While the preferred embodiment of the invention is disclosed anddescribed it will be apparent that various modifications may be madewithout departing from the spirit of the invention or the scope of thesubjoined claims.

I claim:
 1. A method of maintaining isothermal temperature in a sourceusing a baseplate having a plurality of quadrants therein functioning asa heat source, a coldplate including a fluid loop therein functioning asa heat sink, a plurality of radiator panels connected to said fluid loopfor dissipating heat, a plurality of TEHP units each located within oneof said plurality of quadrants in said baseplate thereby coupling eachof said quadrants in said baseplate to said coldplate, and a model basedcontroller individually connected to each of said TEHP units foradjusting the heat pumping capacity thereof, said method including thesteps of:generating waste heat in said baseplate by operating theelectronics, transferring heat across an adverse temperature gradientfrom the baseplate to the coldplate thereby upgrading waste heat,channeling fluid through said fluid loop thereby transferring said heatfrom said coldplate to the radiator panels, sensing a variation intemperature in one of said quadrants in said plurality of quadrants insaid coldplate, and compensating for said variation in temperature insaid one of said quadrants by adjusting heat pumping capacity of saidTEHP units connected to said model base controller.
 2. A method ofperforming decoupled cooling in a source using an augmented thermal bus,wherein a controller individually controls a first, a second and a thirdTEHP units which couples a base plate having a first, a second and athird quadrant therein to a coldplate, said first said second and saidthird TEHP units being individually controlled by a model basedcontroller, said controller including a process, a modelled process andan inverse modelled process, said method comprising the stepsof:measuring temperatures from said first, said second and said thirdquadrants thereby producing a process temperature array, combining saidprocess temperature array with a modelled temperature array produced bysaid modelled process, said combination producing an error temperaturearray, combining said error temperature array with a set pointtemperature array thereby producing an expected inverse model array,inputting said expected inverse model array into said inverse modelthereby producing an array of adjusted currents, inputting said adjustedcurrents into said process whereby a change in the pumping capacity ofsaid first, said second, and said third TEHP units occurs therebyproducing decoupled heat control in said first, said second, and saidthird quadrants, and inputting said adjusted currents into said modelledprocess whereby a change in the pumping capacity of said first, saidsecond, and said third TEHP units is modelled thereby modelling saiddecoupled heat control of said first, said second, and said thirdquadrants.
 3. A process for maintaining isothermality in an augmentedthermal bus, said process comprising the steps of:measuring a first setof parameters in said augmented thermal bus thereby defining an actualprocess of said augmented thermal bus, said actual process includingactual parameters of said augmented thermal bus, modeling said actualprocess of said augmented thermal bus thereby defining a modelledprocess of said augmented thermal bus said modelled process includingmodelled parameters of said augmented thermal bus, performing an inverseof said modelled process for said augmented thermal bus, therebydefining an inverse process for said augmented thermal bus said inverseprocess including inverse parameters of said augmented thermal bus,combining the actual parameters of said augmented thermal bus with saidmodelled parameters of said augmented thermal bus thereby denoting adeviation in isothermality of said augmented thermal bus, combining saiddeviation in isothermality of said augmented thermal bus with a setpoint temperature thereby producing an expected inverse model of saidaugmented thermal bus and compensating for said deviation inisothermality of said augmented thermal bus, and maintainingisothermality in said augmented thermal bus by utilizing said expectedinverse model as input to said inverse modelled process therebyproducing an output which adjust said first set of parameters in saidaugmented thermal bus.
 4. A process as claimed in claim 3 wherein saidfirst said of parameters are temperature measurements.
 5. A process asclaimed in claim 3 wherein said output which adjust said first set ofparameters are voltage measurements.
 6. A process as claimed in claim 3wherein said output which adjust said first set of parameters arecurrent measurements.